This is an adapter plate to mount a buttkicker LFE to the armrest strut of most gaming chairs.

In order to use this adapter, you must open the fusion360 file, and edit Sketch4 under the top level object. The location of sketch 4 is shown in the picture below. I know it isn't very elegant to have to change a sketch, but that is what I had to do to fit it to my sucky drill job